<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<div id="app">
    {{msg}}
</div>

</body>
<script src="https://cdn.jsdelivr.net/npm/vue@2/dist/vue.js"></script>
<script>
    const app = new Vue(
        {
            el: '#app',
            data: {
                "msg": "Hello World!"
            }
        }
    )

    app.msg = '我是李紫坤！'
</script>
</html>